1. Field of the Invention
Aspects of the present invention relate to an air breathing fuel cell stack, and an end plate adopted in the stack, capable of simplifying and thinning a system.
2. Description of the Related Art
Mobile devices, such as, a cellular phone, an MP3 player, a portable multimedia player (PMP), and a notebook computer, etc., are widely used. However, more compact and higher-performance mobile device are in demand. At present, mobile devices are not supplied with sufficient power to support advanced functions, such as, multimedia communication, and digital multimedia broadcasts, etc.
At present, most mobile devices use a lithium ion battery as a main power supply. When a lithium ion battery is charged once, it has an average useable operating time of six hours, in a notebook computer, and about two to three days in a cellular phone. However, since multimedia functions of mobile devices are increasing, the amount of power used to drive the devices has increased, and operating times have been greatly shortened. Therefore, a need exists for a new power supply apparatus.
A fuel cell generates current by directly converting a fuel, for example, hydrogen, into electrical energy. Fuel cells have been identified as power supply apparatuses for mobile devices, because fuel cells produce energy for long periods of time, and can be more easily recharged, as compared to existing lithium ion batteries.
One type of fuel cell, which is suitable for use as the power supply apparatus for a mobile device, is a polymer electrolyte fuel cell (PEFC). Polymer electrolyte fuel cells can be classified as polymer electrolyte membrane fuel cells, proton exchange membrane fuel cells (PEMFC), and a direct methanol fuel cells (DMFC), in accordance with the kind of fuel used therein. Since the polymer electrolyte fuel cell uses a solid polymer as an electrolyte, it has no risk of corrosion or evaporation, due to the electrolyte, and can obtain a high current density per unit area. Moreover, the PEMFC has advantages of very high output, and low operating temperatures, as compared to other kinds of fuel cells. Meanwhile, the DMFC has advantages over the PEMFC, in that the DMFC directly uses a liquid-phase fuel, such as, methanol, etc., without using a fuel reformer, and has an operating temperature of less than 100° C.
The PEFC includes a membrane electrode assembly (MEA), which includes an anode electrode, a cathode electrode, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode. The PEFC has a stack structure in which: an anode separator, including a fuel flow field, to supply fuel to the anode electrode; a cathode separator including an oxidant flow field, to supply an oxidant to the cathode electrode, and the MEA are stacked together. The anode and cathode separators can include different structures, in accordance with the structure and scheme of the fuel cell, and are referred to as bipolar plates.
A PEFC can be classified as an active-type fuel cell, or a passive-type fuel cell, in accordance with a supply scheme of the fuel and the oxidant. The active-type fuel cell has elements that actively supply the fuel to the anode and the oxidant to the cathode. The passive-type fuel cell has a structure that passively supplies the oxidant to the cathode, using ambient air. The passive-type fuel cell is commonly referred to as an air breathing fuel cell. Since the air breathing fuel cell does not include an apparatus to supply the oxidant, it is generally more compact, and operates with less noise.
However, there is a need to provide an air breathing fuel cell that is more compact, but still meets a user's needs. Further, in the air breathing fuel cell, connecting portions to electrically connect a plurality of unit cells, in series, project from a cathode current collector and an anode current collector, to the outside. As a result, the projecting portions increase the volume of the apparatus, a further insulating process is required, and manufacturing is complicated.